Final answer:
The heat energy across an electrical arc is produced by the resistance to current flow across the arc, as described by Ohm's Law and illustrated by the formula P = V²/r, emphasizing the role of resistance in generating heat.
Step-by-step explanation:
The heat energy across an arc is primarily produced by the resistance to current flow across the arc. This resistance converts electric energy into thermal energy, resulting in the generation of heat. Ohm's Law states that the current flowing through most conductors is directly proportional to the voltage applied to them. The formula for electric power, P = V²/r, where P is power, V is voltage and r is resistance, also explains how an electrical arc can generate significant amounts of heat, especially if the resistance is low, as in the case of a short circuit.
Now, to address the side question about resistance, the correct definition is that resistance is the property of materials to resist the passage of electric current. Electric energy conversion to thermal energy can be undesired, as it may lead to heating effects potentially causing damage, such as melting or igniting materials.